Seems like I find more things to say----There are two basic way that trailers are assembled:

1. The base is welded together, then the sides and roof are usually riveted to the base. Using this method, all the stresses are on the base and the sides aren't really "load bearing". This requires a much heavier base frame---more weight.

2. The base and sides are "load bearing" and are welded as a unit. The top is usually welded on as a unit as well. This results in a lighter trailer with the same load bearing strength. It also produces less flex going down the highway.